monarchs have been spotted in south texas. last year, seth doane reported their population was down 75%. but tonight he tells us they're making a comeback. >> reporter: hundreds of millions of monarch butterflies cluster for warmth in these trees every winter. we were clearly impressed when we visited mexico last year. there are an estimated 250 million monarch butterflies that winter in this preserve. that sounds like a lot, it certainly looks like a lot. but the butterfly population we saw was actually at an all-time recorded low as overdevelopment and illegal logging decimated the forests. this year, the trees were dripping in butterflies and the skies filled with millions more monarchs. butterfly colonies covered nearly ten acres of forest-- double the area last year. conservationist bill toone says that's great news, but... >> all that has to be kept in perspective with the fact that last year was the lowest number of butterflies in mexico since we started recording in 1993. >> reporter: why the rebound? the mexican government has made progress fighting illegal logging, down 97%.